A bomb threat received overnight caused school officials in a Salem County school district to cancel classes for the day.

Officials with the Woodstown-Pilesgrove Regional School District said Thursday that a bomb threat from an “unknown source” came in overnight. This prompted officials to close all schools in the district as a precaution. After-school and sports activities were also canceled.

The district has four schools and services students from Alloway Township, Oldsman Township, Pilesgrove Township, Upper Pittsgrove Township and Woodstown.

Officials say that each school will be checked to make sure it is safe before classes resume on Friday.